Multi-Objective Circular Economy Optimisation for Seismic Retrofit of Reinforced Concrete Shear Walls

Growing global demand for resilient and sustainable infrastructure requires seismic retrofit strategies that simultaneously enhance structural performance and minimise environmental impact. This study presents a multi-objective optimisation framework that integrates circular economy (CE) indicators with seismic performance evaluation for the retrofit design of reinforced concrete (RC) shear walls. Nonlinear finite element simulations were carried out in SeismoStruct to evaluate a 125 mm thick component-level RC shear wall strengthened using three techniques: carbon-fibre-reinforced polymer (CFRP) overlays, externally bonded steel plates, and RC jacketing. Structural performance was assessed through nonlinear pushover and cyclic analyses interpreted using the Eurocode 8 N2 method and the ASCE 41–23 displacement coefficient method, while environmental and circularity performance was quantified using the Material Circularity Index (MCI), the Carbon Equivalence Damage Index (CEDI), and a Design for Circularity (DfC) score. A Non-dominated Sorting Genetic Algorithm II (NSGA-II) was used to generate Pareto-optimal retrofit solutions across four objectives: seismic capacity, embodied carbon, retrofit cost, and material circularity. Results show lateral-capacity increases of approximately 50–75% for steel strengthening and RC jacketing, while CFRP overlays leave the flexural capacity unchanged but double the shear capacity: steel plate strengthening provides the highest structural capacity and circularity performance (MCI=0.45, DfC=8.7/10), RC jacketing yields the greatest stiffness gain but the lowest circularity (MCI=0.08), and CFRP overlays offer the most balanced structural, environmental, and economic performance. The framework was validated on a six-storey RC building containing 200 mm thick shear walls, confirming that integrating seismic assessment with circular economy indicators supports more sustainable and resilient retrofit decision-making.